A calibration system is disclosed for a stereoradiographic device having an X-ray source and a vertical X-ray receiver, the calibration system includes a horizontal table which rotates between two reference positions that are separated by 90 degrees in a horizontal plane of the table. A vertical frame is fastened to the horizontal table and is symmetrical with an axis of rotation of the table, the frame accommodates a patient that remains stationary relative to the frame as the table is rotated between its two reference positions wherein corresponding X-ray photographs are taken. At least three markers made of radio-opaque material are firmly attached to the frame, one of the markers represents the origin of orthogonal X,Y and Z axes, a second of the markers is located at a predetermined point along the X-Y axes, the third marker located at a known distance along the Z axis, the markers defining respective distances Lx, Ly or H relative to the origin.